1. Field of the Invention
The invention relates to an exhaust gas control device of an internal combustion engine.
2. Description of the Related Art
Exhaust gas in internal combustion engines such as diesel or gasoline engines contains, for instance, components such as carbon monoxide (CO), unburned fuel (HC), nitrogen oxides (NOx) and particulate matter (PM: particulates).
An exhaust treatment device is mounted in the internal combustion engine in order to purify these components. The exhaust treatment device has, for instance, an oxidation catalyst for oxidizing CO and the like, a NOx storage catalyst or NOx selective reducing catalyst for removing nitrogen oxides, and an particulate filter for removing particulate matter.
Generation of flame in the exhaust purification device of an internal combustion engine is a conventional feature. Published Japanese Translation of PCT Application No. 8-509044 (JP-A-8-509044) discloses a device that includes a fuel supply body, and a fuel line which is provided in the gas discharge line of exhaust gas of the engine and which supplies fuel that ignites at a low temperature. The device has also an air pump that supplies combustion air, via an air line, into the gas line of the exhaust gas. Particulate pollutants in the exhaust gas stream are burned off in an exhaust gas pipe upstream of a particle filter for removing particulate pollutants.
Published Japanese Translation of PCT Application No. 2000-514911 (JP-A-2000-514911) discloses a combustion chamber that has a first catalytic reactor and a second catalytic reactor disposed in series with the first catalytic reactor. The first catalytic reactor is heated to or above ignition temperature. Thereafter, a fuel and air mixture is infused into the first catalytic reactor. Catalytic combustion begins thereby in the first catalytic reactor. The flow rate of air-fuel (A/F) mixture is increased after ignition at the first catalytic reactor, and catalytic combustion moves onto the second catalytic reactor, as a result of which there is heated a heat exchanger for heating that is disposed downstream of the second catalytic reactor.
The temperature of the exhaust treatment device can be raised in a short time through generation of flame upstream of the exhaust treatment device. The temperature of the exhaust gas is raised through flame generation, so that the temperature of the exhaust treatment device can be raised by way of the resulting high-temperature exhaust gas. For instance, the temperature of an oxidation catalyst can be raised to the activation temperature, in a short time, through flame generation upstream of the oxidation catalyst.
To generate flame in an exhaust passage, the flame can be generated, for instance, by heating unburned fuel that is supplied into the exhaust pipe. Flame generation upstream of the exhaust treatment device allows the temperature of the exhaust gas to be raised and allows also reforming the combusting fuel. For instance, flame generation allows reforming heavy unburned fuel into light unburned fuel. A light reducing agent having excellent reducing power can be supplied thereby when it is necessary to supply a reducing agent into the exhaust treatment device.
Flame generated through fuel combustion gives rise to highly reactive substances (active substances) within the flame. These substances include, for instance, radicals and intermediate products. These active substances have strong oxidizing or reducing power, and are therefore appropriate for oxidation reactions and reduction reactions in the exhaust treatment device. The active substances in the flame, however, are unstable, and turn at once into stable final products outside the flame. Flame-generated active substances have been overlooked in the related art, and have not been sufficiently exploited.